Method for distinguishing between nylon polymer having different dye depths



3,387,943 METHOD FOR DISTINGUISHING BETWEEN NYLON POLYMER HAVING DIFFERENT DYE DEPTHS Tom D. Gritlin, Pensacola, and James B. McKay, In, Cottage Hill, Fla, and Leonard L. Millar, Westport, Conn., assignors to Monsanto Company, St. Louis, M0., a corporation of Delaware No Drawing. Filed July 13, 1965, Ser. No. 471,726 10 Claims. (Cl. 23230) The invention herein described and claimed is a method for distinguishing between polymer capable of being deeply dyed and nylon polymer which does not dye as deeply.

In a recent development yarns made from polymer of the same general chemical composition have been developed which have different dye depths. More readily dyeable yarn in comparison with regular yarn of the same general chemical composition is termed deeper-dyeing yarn. Combinations of deeper dyeing yarns with regular yarn in the same fabric produces highly attractive tone-ontone color patterns even when dyed in a single dye bath. It has become possible to produce multiple color patterns with a single dye bath. The many possible colors when combined with the innumerable possible geometric patterns makes it possible to produce a limitless number of -1 color-pattern combinations.

Yarn made from nylon polymer can be made to have variable dye depths by incorporating small quantities of certain additives therein. Nylon as used herein is a longchain polymeric amide having recurring amide groups as an integral part of the main polymer chain, and is capable of being formed into a filament in which the structural elements are oriented in the direction of the axis. Nylon includes nylon-66 (polyhexamethylene adipamide), nylon- 6 (polymeric 6-amino caproic acid), nylon-610 (polyhexamethylene sebacamide), nylon-4, nylon-7, nylon-11, etc., and fiber-forming co-polymers thereof. By incorporating small quantities of N-substituted aminoalkyl piperazines in which the alkyl group contains from 1-6 carbon atoms into nylon polymer, yarn made therefrom can be made more deeply dyeable than yarn made from polymer containing no N-substituted aminoalkyl piperazine. Examples of N-substituted aminoalkyl piperazines include N-aminomethyl piperazine, N-arninoethyl piperazine, and N,N-bis(aminopropyl)piperazine. Generally the N-substituted aminoalkyl piperazines are present in polymer (and, of course, in yarn made from such polymer) in a concentration of at least 0.1 weight percent. Because of its commercial availability N-aminoethyl piperazine is most frequently employed as an additive to make nylon polymer, thus yarn, more deeply dyeable.

Deeper-dyeing nylon polymer and regular-dyeing nylon polymer have no readily perceptible characteristics that differ sufficiently to make yarn made from the two kinds of polymer readily distinguishable from one another. That is, the color, strength, handle, etc. of the two yarns are so similar that they cannot be easily distinguished either by sight or by touch. This lack of ready identification creates problems that significantly hamper producers and users of deeper-dyeing nylon yarn.

The most common problem occurs in textile mills. In order to achieve the geometrical pattern and color harmony desired by the fabric designer, deeper-dyeing yarn ends must be precisely in a prescribed position relative to regular dyeing yarn ends. Otherwise, the finished, dyed fabric will contain dye streaks that break the geometrical pattern and distort the color harmony, making the fabric undesirable. Since deeper-dyeing and regular yarn look alike, occasional errors in placement of yarn ends are unavoidable.

The common method of checking the placement of yarn ends is to knit or weave several yards of fabric, then States Patent 3,387,943 Patented June 11, 1968 shut down the machine while the sample fabric is submitted to a regular scouring and dyeing treatment; any improperly positioned ends revealed in the dyed fabric are then corrected on the machine before proceeding. This is a reliable method, but very costly and cumbersome. Production is halted while the dyeing procedure is carried out, and the test fabric itself is largely wasted as a dowugraded remnant.

Applicants have discovered a relatively simple method of making deeper-dyeing nylon, especially nylon-66, polymer containing a N-aminoalkyl piperazine visually distinguishable from nylon polymer not containing such additive. The method of the invention eliminates or greatly mitigates the problems encountered in handling deeperdyeing nylon yarn. The instant method is applicable to bulk nylon polymer chips as well as to light denier and heavy denier yarns made from nylon polymer and to fabric constructed from these yarns.

The method of the invention comprises applying methyl red to the surface of nylon polymer as well as to yarn or fabric made therefrom. If the polymer contains an N- aminoalkyl piperazine, the methyl red changes in color. The methyl red remains substantially unchanged in color if the polymer does not contain an Nnminoalkyl piperazine. The distinct color contrast makes deeper-dyeing yarn visually distinguishable from regular dyeing yarn.

The color difference is readily seen if the N-aminoalkyl piperazine is present in the polymer at a concentration of at least 0.1 percent by weight. At very low concentrations the color change is to pink. As the concentration increases, the color change is from red to pink to differing, ever deepening, shades of yellow until lemon yellow obtains. The methyl red color change appears to be specific to the presence of N-aminoalkyl piperazine in the deeper dyeing polymer; however, the reasons for this action are not understood. Neither the presence of ordinary finishes or lubricants on yarn nor re-heatFng or heat-setting thereof affects the color change of methyl red applied thereto or to greige fabric made therefrom. On the other hand, if deeper-dyeing yarn or fabric is given a mild scouring or leaching treatment, methyl red undergoes no color change when applied to the yarn or fabric. Presumably this leaches the N-substituted aminoalkyl piperazine from the polymer surface. A large number of other indicator dyestuffs, such as methyl orange, Chlor Phenol Red, Brom Cresol Green, Brom Thymol Blue and Phenol Red, were all applied unsuccessfully; methyl red alone provided a discernible color change.

Because it is almost completely insoluble in water, methyl red is dissolved in an aqueous solution containing alcohol, the. lower alkyl alcohols (1 to 3 carbon atoms), such as methanol, ethanol, n-propanol and isopropanol, being particularly suitable. Of course, alcohol alone as well as ether and other like solvents could be used, but it is more desirable to use an aqueous alcohol solution as the methyl red solvent. A 50-70% aqueous alcohol solution is most preferred.

The methyl red concentration in the solvent is not highly critical. Nevertheless, with a concentration of less than 0.005 weight percent the color contrast is weak. There is no gain in color contrast when the methyl red concentration is increased beyond about 0.07 weight percent. The general concentration range for effective use is therefore 0.005 to 0.07 Weight percent, the preferred range being 0.01 to 0.04 weight percent.

The methyl red may be applied to polymer at any desirable point in the yarn spinning or textile manufacturing operations prior to scouring the greige fabric. Application may be made by swabbing, daubing, brushing or spraying. The most convenient method of applying the methyl red solution is to spray it from a hand-operated atomizer or from an aerosol bomb especially prepared for this purpose.

Methyl red is applied to yarn in the yarn packaging operation to check. the yarn end positions in section beams or warps, and is applied to the first portion of knitted or woven fabric to insure that yarn ends are properly threaded to yield the desired fabric pattern. Methyl red is applied to only a small portion of the yarn or fabric, and none of the yarn or fabric so tinted is downgraded in the process, the residual methyl red being completely scourable in the standard fabric finishing treatment.

The following examples are set forth to illustrate the invention. It is not intended that the invention be limited by their inclusion in any manner whatsoever. All percent figures are weight percent unless noted to the contrary.

EXAMPLE I A series of nylon-66 polymer samples were prepared by the conventional, well-known batch polymerization method. Various additives known to impart deeper-dyeing characteristics to nylon-66 polymer were incorporated in the various polymer samples during the polymerization. The resultant polymer samples were extruded into a ribbon which was solidified and cut into chips or flake suitable for remelting and conversion into shaped articles, such as filaments. Samples of each type of polymer were sprayed lightly with a methanol-water solution of methyl red (0.1 gm. of methyl red per liter of solution). The colors imparted to the polymer chips were as follows:

Polymer Color Imparted Sample Wt. Percent Additive in Polymer by Methyl Red Number 1 No additive 2. 0.75% benzene phosphinie acid 3. 0.125% N-aminoethyl piperazin Pale pink.

4- 0.25% N-aminoethyl piperazine Very light yellow.

5 0.50% N-aminoethyl piperazine.-. Lemon yellow.

6 6.0% caprolaetam R d e 7 0.25% N ,N-bis(eminopropybpipera- Lemon yellow.

zine.

Prior to being sprayed with methyl red the various polymer samples were visually indistinguishable. It is evident from the above that the color change is due to the presence of a N-substituted aminoalkyl piperazine in the Polymer.

EXAMPLE H EXAMPLE H1 The 70 denier yarns of Example II were used to knit a fabric on a warp knitting machine, the fabric alternat ing bands or stripes of varying width composed of 2 to 8 ends of standard nylon yarn followed by 2 to 8 ends of deeper-dyeing yarn. The greige fabric appeared ur1iformly white, the stripes composed of deeper-dyeing yarn being practical indistinguishable visually from the stripes composed of regular yarn.

A portion of the knit fabric was sprayed lightly with methyl red solution prepared in the following manner: 0.5 gm. of methyl red was dissolved in a solution consisting of 2.5 liters of isopropanol, 1.0 liter of methanol and 1.5 liters of deionized water. Upon contact with the methyl red solution the deep-dyeing yarn in the fabric turned lemon yellow while the regular yarn became red, showing clearly an alternating striped pattern of the fabric and the identity of the yarn type included in each stripe. Any mis-positioned yarn ends were easily located.

EXAMPLE IV Standard nylon-66 polymer was produced with conventional continuous polymerization equipment, the polymer being pumped directly to multiple spinning heads where it was extruded into a 68-filament yarn having a total denier of 4200, individual filaments having an unsymmetrical trilobal cross section.

Deeper-dyeing yarn was spun similarly to the above standard nylon yarn, the additive material being injected continuously into the reactant stream at the appropriate points in the polymerizer train. The nylon-66 polymer included these additive materials: 0.75% benzene-phosphinic acid, 8.75% caprolactam, and 0.23% N-aminoethyl piperazine. were drawtwisted and texturized by a commercial gearteXturing operation to yield 68-filament bulked yarn having nominal total denier of 1230. Two ends of 1230 denier yarn were then plytwisted together to form nominal 2460 denier yarn suitable for tufted carpet fabric. Ends were plyed together in the following combinations: two ends of regular nylon, one end of regular and one end of deeper-dyeing yarn, and two ends of deepeudyeing yarn, providing three different types of 2460 denier-13d filament carpet yarns.

Ends of the 2460 yarns were drawn through the needles of a 168-needle, inch gage, loop pile tufting machine. Ends were arranged to provide a pattern with a repeating sequence of adjacent tufts across the width of the tufted fabric: regular, mixed regular-deeper-dyeing, deeperdyeing, mixed regular-deeper-dyeing, regular, etc. Dyed in a single dye bath this fabric displayed a tone-on-tone pattern of stripes along the length of the fabric. When sprayed with the methyl red solution described in Example IH, the greige tufted fabric assumed highly contrasting red and yellow surface colors making the identity of each yarn type immediately evident. Whether applied on the tufted face side or on the pulled-down back side of the fabric, the yellow-red color contrast between deeperdyeing and regular nylon yarn ends made identification very simple. Misplaced ends or offsets in the pattern could immediately be corrected on the tufting machine.

The advantage of the invention is readily apparent. It is extraordinarily simple to distinguish between deeperdyeing polymer, yarn made from such polymer, and fabric made from such yarn and the same items made from standard, non-deeper-dyeing nylon polymer.

Although the invention has been described by reference to particular examples, embodiments, compounds and the like, it should be broadly construed and should only be limited by the appended claims.

What is claimed is:

1. A method for distinguishing between deeper-dyeing nylon polymer containing at least one N-substituted aminoalkyl piperazine and nylon polymer containing substantially no N-substituted aminoalkyl piperazine comprising applying methyl red to both of said polymers whereby the methyl red applied to said deeper dyeing polymer undergoes a substantial color change while the methyl red applied to said polymer containing substantially no N-substituted aminoalkyl piperazine remains substantially unchanged in color.

2. The method of claim 1 wherein in methyl red is applied in an aqueous solution of a lower alkyl alcohol containing from 1 to 3 carbon atoms.

3. The method of claim 1 wherein the nylon is nylon-66.

4. The method of claim 1 wherein the N-substituted aminoalkyl piperazine is N-aminoethyl piperazine.

5. The method of claim 1 wherein the alkyl group of 5 the N-snbstituted aminoalkyl piperazine contains from 1 to 6 carbon atoms.

6. The method of claim 5 wherein the N-substituted aminoalkyl piperazine is N-aminoethyl piperazine.

7. A method for distinguishing between deeper-dyeing yarn made from nylon polymer containing at least one N-substituted aminoalkyl piperazine and yarn made from nylon polymer containing substantially no N-substituted aminoalkyl piperazine comprising applying methyl red to both of said yarns whereby the methyl red applied to said deep-dyeing yarn undergoes a substantially color change while the methyl red applied to said yarn made from nylon polymer containing substantially no N-substituted aminoalkyl piperazine remains substantially unchanged in color.

8. The method of claim 7 wherein the alkyl group of the N-substituted aminoalkyl piperazine contains from 1 to 6 carbon atoms.

9. The method of claim 7 wherein the methyl red is applied in an aqueous solution of a lower alkyl alcohol containing from 1 to 3 carbon atoms.

10. The method of claim 7 wherein the nylon is nylon-66.

No references cited.

MORRIS O. WOLK, Primary Examiner.

E. KATZ, Assistant Examiner. 

1. A METHOD FOR DISTINGUISHING BETWEEN DEEPER-DYEING NYLON POLYMER CONTAINING AT LEAST ONE N-SUBSTITUTED AMINOALKYL PIPERAZINE AND NYLON POLYMER CONTAINING SUBSTANTIALLY NO N-SUBSTITUTED AMINOALKYL PIPERAZINE COMPRISING APPLYING METHYL RED TO BOTH OF SAID POLYMERS WHEREBY THE METHYL RED APPLIED TO SAID DEEPER DYEING POLYMER UNDERGOES A SUBSTANTIAL COLOR CHANGE WHILE THE METHYL RED APPLIED TO SAID POLYMER CONTAINING SUBSTANTIALLY NO N-SUBSTITUTED AMINOALKYL PIPERAZINE REMAINS SUBSTANTIALLY UNCHANGED IN COLOR. 